1. Field of the Invention
The present invention relates to an image processing apparatus that processes image data representing an image to be formed on a recording medium, and a method thereof.
2. Description of the Related Art
An electrophotographic type image forming apparatus is an example of an apparatus that forms an image on a recording medium. In electrophotography, first, a charging unit uniformly charges a photosensitive member, which is an image bearing member. Then, an exposure unit scans the photosensitive member with an optical beam such as a laser according to an image signal to form an electrostatic latent image on the photosensitive member. Next, a developing unit develops the electrostatic latent image formed on the photosensitive member to form a toner image thereon. Then, generally, the toner image developed on the photosensitive member is primarily transferred onto an intermediate transfer member, and then secondarily transferred from the intermediate transfer member onto a recording medium. A fixing unit fixes toner on the recording medium by heating and pressing the transferred toner image to form an image on the recording medium.
Recently, various types of recording media are used in electrophotographic type image forming apparatuses, and depending on the type of recording medium, it is known that defects can occur during the transfer step or the fixing step. It is known that, especially in the case of drawing a fine line of about several tens micrometers to several hundred micrometers width, which is used in drawings and letters, on recording media having large surface unevenness, discontinuity or irregularity of lines, or a recording density decrease may be caused.
Japanese Patent Application Laid-Open No. 2011-257727 discusses a technique for controlling at least one of halftone processing, exposure intensity, and developing bias based on the unevenness state of the paper surface. For example, if the paper surface unevenness is large, in consideration of a decrease in the toner transfer amount (a transfer defect) at depressed portions, the dot size is relatively increased at depressed portions compared with that for paper having a flat surface.
However, for a fibrous recording medium like paper, the frequency characteristic of the surface unevenness is different depending on the thickness of the fibers, and fine line reproducibility also changes. In the method discussed in Japanese Patent Application Laid-Open No. 2011-257727, while control is performed in consideration of the surface unevenness of the recording medium, consideration is not given to the frequency characteristic of the recording medium. Therefore, the appropriate fine line processing is not always performed.